336,000,000 Coins are available. And right now 184,845,880 are in circulation. This just means that not all feathercoins are found yet and that we can still mine them.
For example Bitcoin has 21,000,000 Coins and 16,738,612 are in circulation. So they are closer to the point where it is impossible to mine new bitcoins. When they reach 21 Million coins it is impossible to mine new coins. Miners will only get paid by fees when that happens because new bitcoins can’t be generated anymore.